The Great Mimicker . . .

An Olympic Gold Moment

By Marilyn Sarina, BMLSc, ART, MT(ASCP), CLS Supervisor, Central Coast Pathology San Luis Obispo, California

here is no doubt that one of the most capable of contaminating its Tinteresting aspects of working in surroundings survives. microbiology involves those rare occasions when we come upon an isolate that will probably only be seen once in our careers. We like to think of it as “Our Olympic Gold Moment”. This recent occurrence in our laboratory created an enthusiastic educational opportunity, to say the least.

Our excitement involved the isolation and identification of an organism termed the “Vietnamese Time Bomb” and the Figure 1: The disease, melioidosis, is most causative agent is Burkholderia commonly found in Southeast Asia, especially pseudomallei. B. pseudomallei is an Thailand. The causative agent, Burkholderia organism that has been considered a pseudomallei can be found in soil and water. potential agent for biological warfare and terrorism. Transmission occurs by direct contact with contaminated soil and surface The organism is an aerobic gram- waters. Melioidosis, sometimes called negative bacillus that causes melioidosis, “The Great Mimicker”, manifests itself which is predominantly a disease of clinically as abscesses, pneumonia, and tropical climates. It is endemic in at worst, as a fatal septicemia in Southeast Asia, Northern Australia, and susceptible hosts. The incubation period other tropical and non-tropical regions. (time between exposure and appearance Today, it can be imported to regions of clinical symptoms) is not clearly with inappropriate climate if a carrier defined but may range from two days to many years.

Our case involved an abscess from the middle finger of an otherwise healthy 27 year old female. The abscess was drained and a sample was sent to our laboratory for routine culture.

Figure 3: Close-up of colonies of B. pseudomallei on blood agar. Note the wrinkled “cornflower” appearance which may not be Figure 2: Mature colonies of B. pseudomallei on apparent before 3-5 days growth. MacConkey Agar. Pseudomonas stutzeri can be confused with B. pseudomallei due to its similar colony We recovered a light growth of cream- morphology. colored colonies after 48 hours of incubation. By 72 hours, the colonies From this point onward, all subsequent displayed the characteristic “cornflower” manipulations were performed under a morphology (see photos). Laboratory biological safety cabinet as a identification of B. pseudomallei can be precautionary method. The isolate was difficult, especially in western countries then forwarded to the San Luis Obispo where it is rarely seen. Biochemically, County Public Health Laboratory for the isolate was oxidase positive, indole confirmation of our findings. PCR positive, catalase positive, arginine (polymerase chain reaction) testing dehydrolase positive, motile, and confirmed the identification as that of B. produced nitrate gas. Our automated pseudomallei. identification system yielded an excellent biotype (97% probability) for Most cases of melioidosis can be treated B. pseudomallei. with appropriate antibiotics. Treatment should be initiated early in the course of the disease.

It has been a common pathogen isolated from troops of all nationalities that have served in areas with endemic disease, but is rarely isolated on U.S. soil in the absence of travel to endemic areas.

Marilyn Sarina, BMLSc, ART, MT(ASCP), CLS

Figure 5: Melioidosis has been called the "great mimicker" because its effects—including septicemia, abscesses; and lung, kidney, and heart disease—are remarkably wide-ranging, making diagnosis difficult.

Figure 4: The genetic plasticity of Burkholderia pseudomallei (stained red) allows it to adapt to different environments and to cause multi- faceted disease in humans. (Photo credit: Mark P. Stevens, PhD/Institute for Animal Health)